Method for continuous production of dihydroxydiarylalkanes

ABSTRACT

The present invention relates to a process for the continuous production of dihydroxydiarylalkanes (bisphenols) by the reaction of fresh phenol, phenol and isoalkenylphenol from the decomposition of by-products, and ketone. In this process the bulk of the bisphenol is recovered from the reaction mixture by crystallization and the mother liquor obtained is freed from phenol by distillation. The phenol is returned to the reaction and the bottoms obtained during the distillation are decomposed in a reactive rectification after addition of a basic catalyst. The phenol and isoalkenylphenol leaving at the top are led back into the reaction; the bottoms from the first reactive column are acidified and in a second reactive rectification, in the presence of an acid catalyst, are further decomposed into phenol, which distils off and is reused in the reaction, and bottoms, which are disposed of.

The present invention relates to a process for the continuous productionof dihydroxydiarylalkanes (bisphenols) by the reaction of fresh phenol,phenol and isoalkenylphenol from the decomposition of by-products, andketone. In this process the bulk of the bisphenol is recovered from thereaction mixture by crystallisation and the mother liquor obtained isfreed from phenol by distillation. The phenol is returned to thereaction and the bottoms obtained during the distillation are decomposedin a reactive rectification after addition of a basic catalyst. Thephenol and isoalkenylphenol leaving at the top are led back into thereaction; the bottoms from the first reactive column are acidified andin a second reactive rectification, in the presence of an acid catalyst,are further decomposed into phenol, which distils off and is reused inthe reaction, and bottoms, which are disposed of.

The production of bisphenols by the-acid-catalysed reaction of ketoneswith phenol is known. There have been a number of different proposalsfor this (cf., for example, U.S. Pat. Nos. 2,775,620, EP-A 342 758, EP-A616 993, DE-OS 3 833 900, 4,308,404, 4,308,405, EP-A 630 878, U.S. Pat.Nos. 4,876,391, 3,242,219).

There is a survey of the older literature on bisphenol production inUllmann's Encyclopedia of Indust. Chem., 5th. Edition, Vol. A 19, pages348-52. As a rule bisphenols, especially bisphenol A (BPA), industriallythe most important of the bisphenols, are prepared by introducing ketoneand phenol into a recirculated mother liquor obtained from the workingup of bisphenol, this mixture is passed through acidic ion exchangersand the conversion to bisphenol takes place. Any ketone which maypossibly not have reacted is recovered from the reaction mixture and ledback into the reaction. The reaction mixture is cooled, the bisphenol isif necessary allowed to crystallise out as phenol adduct, separated offand washed with phenol. The phenol is separated from the adduct by flashdistillation and pure bisphenol is recovered. The mother liquor from thecrystallisation is passed through acidic ion exchangers and isomerscontained therein undergo rearrangement to form bisphenol. The bisphenolthus formed is separated by crystallisation and the crystallisateobtained is passed to the first crystallisation step. A portion(approximately 10 to 20%) of the mother liquor now obtained is setaside; the bulk is returned to the reaction. Phenol is distilled offfrom the portion set aside and is returned to the reaction. The residueobtained during the distillation is removed from the process and isused, for example, for the preparation of phenol resin.

In this procedure, which is relatively complicated, the mother liquor isrepeatedly passed over the catalyst. In the course of this many isomersand by-products are formed, as well as coloured compounds which have tobe carefully removed from bisphenol, which may necessitate a furthercrystallisation. Secondly, an appreciable quantity of valuablecompounds, such as bisphenol and isomers, are lost in the portion whichis set aside and ultimately discharged. This removal from the motherliquor is absolutely essential, so as not to allow the quantity ofunusable and interfering compounds to become too great.

Attempts have therefore been made to work up and to decompose thedischarged portion, in order to recover the valuable materials for usein the production of bisphenol. For this, too, there have been a numberof different proposals. By pyrolysis at about 300° C. it is possible toobtain moderate yields of phenol and alkylphenols, which have still tobe thoroughly purified (U.S. Pat. No. 2,497,503). A hydrogenationtreatment also leads to valuable products, as is disclosed in EP-A 17852. The decomposition can also be accelerated by acidic and basiccompounds. However, only phenol is obtained by using acids such assulfuric acid or toluenesulfonic acid (U.S. Pat. No. 3,466,337). Basiccatalysts, on the other hand, effect a decomposition of the dischargedmaterials into phenol and isoalkenylphenol. Catalysts mentioned arealkali metal compounds, such as NaOH, KOH, NaHCO₃, Na acetate, Nahypophosphite, K₂CO₃, MgO and Al isopropylate (U.S. Pat. Nos. 4,277,628,4,594,459, 4,131,749). In this procedure, however, only a part of thedischarged material is decomposed, and operation is intermittent orsemicontinuous. Wholly continuous processes are unknown.

These processes have been improved, as regards a higher purity of thebisphenol, in that the phenol/isoalkenylphenol mixture from thedecomposition is introduced into the first mother liquor after theseparation of the first bisphenol portion. The mixture is passed overthe acid catalyst and the reaction of isoalkenylphenol with phenol andthe rearrangement are allowed to proceed simultaneously. The secondbisphenol portion is then separated from the mixture by crystallisationand the second mother liquor is again removed for decomposition. Thesecond bisphenol portion is introduced into the first crystallisation.The purity of the bisphenol is thereby somewhat increased, but theprocess is rendered more complicated by an additional circulation (U.S.Pat. No. 4,954,661).

It has also been proposed that the second mother liquor in the bisphenolprocess described above, or the first mother liquor after separation ofthe first quantity of bisphenol and after the rearrangement, be at leastpartly worked up by distillation, in order better to utilise thevaluable products contained therein. The bisphenol thus obtained isreintroduced into the first crystallisation step and purified there. Thelow-boiling components containing isomers are introduced into thereaction (WO 94/20445 and EP-A 552 518). The difficulty lies inobtaining at justifiable expense from the mother liquor, which is highlyenriched by isomers and by-products, sufficiently pure fractionsparticularly low in chromans and indans, which are difficult to remove,without excessively increasing the no longer usable residue anddiminishing the yield. Because of this, a portion of the distillationproducts have to be discarded.

The fractions low in bisphenol which are obtained during thedistillation may also be decomposed and the decomposition productsreintroduced into the process (EP-A 332 203).

It has now been found that an excellent yield of bisphenol of highpurity is obtained by a simple, wholly continuous process, if phenol isreacted with ketone and with isoalkenylphenol from the decomposition insuch a way that as small a quantity as possible of isomers andby-products is formed, unreacted ketone is distilled off from thereaction mixture, acidic components are optionally separated off, thebulk of the bisphenol contained therein is isolated by crystallisation,the mother liquor and the washing phenol from this crystallisation stepare combined, phenol is distilled off and introduced into the reaction,the bottoms are mixed with a basic catalyst and, in a first reactiverectification, are decomposed into phenol and isoalkenylphenol leavingat the top, both of which flow into the reaction, the bottoms obtainedduring the reactive rectification are acidified and, in the presence ofan acid catalyst, in a second reactive rectification are decomposed intophenol, which is introduced into the reaction, and a residue, which isto be disposed of.

Suitable aromatic hydroxyl compounds for the process according to theinvention are not substituted in the para position and contain nosubstituents of the second order, such as cyano groups, carboxyl groupsor nitro groups; examples which may be mentioned are phenol, o- andm-cresol, 2,6-dimethylphenol, o-tert.-butylphenol, 2-methyl6-tert.-butylphenol, o-cyclohexylphenol, o-phenylphenol,o-isopropylphenol, 2-methyl-6-cyclopentylphenol, o- and m-chlorophenol,2,3,6-trimethylphenol. Preferred compounds are phenol, o- and m-cresol,2,6-dimethylphenol, o-tert.-butylphenol and o-phenylphenol; phenol isparticularly preferred.

Suitable ketones contain at least one aliphatic group on the carbonylfunction; examples which may be mentioned are acetone, methyl ethylketone, methyl propyl ketone, methyl isopropyl ketone, diethyl ketone,acetophenone, cyclohexanone, cyclopentanone, methyl-, dimethyl- andtrimethylcyclohexanone, which may also have geminal methyl groups, suchas 3,3-dimethyl-5-methylcyclohexanone (hydroisophorone). Preferredcompounds are acetone, acetophenone, cyclohexanone and its homologuescontaining methyl groups; acetone is particularly preferred. Suitablecatalysts for the basic decomposition are those mentioned in theliterature, preferably alkali metal oxides and hydroxides, particularlypreferably NaOH and KOH. In the process according to the invention, theyare introduced into the melt of the decomposition educts, dissolved andhomogeneously distributed, the temperature expediently being between100° C. and 200° C., preferably 120° C. and 180° C.

Suitable catalysts for the acid decomposition are those mentioned in theliterature, preferably sulfuric acid, phosphoric acid, phosphorous acid,the partial salts thereof, such as NH₄HSO₄, NaHSO₄, KHSO₄, NaH₂PO₄,KH₂PO₄, NH₄H₂PO₄, NH₄H₂PO₃, KH₂PO₃ and analogues, also the organicderivatives of these acids, namely aromatic sulfonic acids anddisulfonic acids, such as benzenesulfonic acid, toluenesulfonic acid,xylenesulfonic acid, phenolsulfonic acid, diphenyldisulfonic acid,diphenyl ether disulfonic acid, then aromatic phosphonic and phosphinicacids, such as benzene-, toluene- xylenephosphonic and -phosphinicacids, diphenyldiphosphonic acid and diphenyldiphosphinic acid, alsosolid acids, such as acidic aluminium oxides, aluminas such asbentonites and montmorillonites, zeolites, titanium oxide and zirconiumoxide, niobium oxide and tantalum oxide; acidic aluminas are preferred.

The quantities of catalysts added to the mixture to be decomposed arefrom 0.01 wt. % to 5 wt. %, preferably from 0.05 to 3 wt. %,particularly preferably from 0.1 to 2 wt. %, based on the quantity ofdecomposed mixture. To render adherence to these specified quantitiespossible in the case of acid catalysts, after the basic decompositionthe basic catalysts must either be removed from the bottoms, which inany event would probably be too expensive, or they must first beneutralised by a strong acid, before the addition of the requiredquantity of acid catalyst takes place. In this way the presence ofsufficient quantities of active acid is ensured. For the purpose of theinvention, acidification therefore means that acid is added to thebottoms from the basic decomposition in a quantity such that both thebasic catalyst contained therein is neutralised and over and above thisthere is available a sufficient quantity of acid catalyst for thesubsequent acidic decomposition.

The catalysts, for example, dissolved or suspended in phenol, may bemetered continuously into the stream flowing in the column wheredecomposition takes place. But it is also possible, in intermediatecontainers, to admix them in batches to the material to be decomposedand then to convey this mixture continuously into the column wheredecomposition takes place.

The columns in which the reactive rectifications are carried outcorrespond to the distillation columns generally used. In the columns,the decomposition takes place beneath the separation by distillation andfractionation of the decomposition products phenol and isoalkenylphenolfrom the undecomposed or perhaps undecomposable compounds. In the courseof this the decomposition products, generally already sufficiently purefor further use, leave at the top. The undecomposable constituents aredischarged as bottoms. Reactive rectifications are known to the personskilled in the art and are described, for example, in Ullmann'sEncyclopedia of Industrial Chemistry, 5th. Edition, Vol. B 4, pages321-8.

In the present case it may be advantageous to decrease the columndiameter appropriately in the lower part of the columns wheredecomposition takes place, to correspond to the decreasing volume ofliquid and gas from top to bottom in the column during thedecomposition. In order to establish a suitable residence time in thecolumn for the material being decomposed, it is useful to insert traysinto the columns where decomposition takes place. This appliesparticularly to the part in which the decomposition proceeds. In theupper part, the use of filler material or packings may be advisable foran effective separation of the products. In the event that the purity ofthe phenol distilling off from the second decomposition column isinadequate for use in the bisphenol synthesis, it may be passed into anadditional column or else into the first decomposition column andfurther purified there. Preferred procedures for the reaction to formbisphenol are those which deliver bisphenol at the highest selectivitypossible. They are distinguished in that the reaction is carried out atthe lowest possible ketone concentration. This can be achieved byreacting phenol with ketone and isoalkenylphenol in at least twoserially connected reactors containing acidic ion exchangers andoperated at as low a temperature as possible, but with increasingtemperatures in the direction of the progressing reaction, the totalquantity of ketone and isoalkenylphenol being apportioned between theindividual reactors and being distributed homogeneously in the reactionmixture before the introduction into the respective reactors. Theselectivity for bisphenol can be further increased if the distributionof ketone and isoalkenylphenol is controlled in such a way that theproportion of the total quantity per reactor is the smaller, the moreelevated the temperature of the respective reactor, and the series ofreactors is operated within a temperature span of at most 35° C. to 85°C., preferably of 38° C. to 75° C.

It is useful to provide mixing units of known type in front of theindividual reactors, in order to ensure the homogeneous distribution ofketone and isoalkenylphenol in the starting phenol and reaction mixturerespectively, as well as heat exchangers for the required tempering ofthe mixture before the passage through the catalyst bed.

After it has left the last reactor of the series and after separation ofunreacted ketone, the reaction product is optionally freed from acidiccomponents, as described, for example, in U.S. Pat. No. 4,876,391 orEP-A 552 518 and optionally subjected to a fine filtration in order toremove dust from the catalyst and from the apparatus or other solidcontaminants. The reaction mixture then flows into a crystalliser, whichis conventionally used for the bisphenol synthesis and is known to theperson skilled in the art (Ullmann's Encyclopedia of IndustrialChemistry, 5th. Edition, Vol. B 2, pages 3-1 to 3-34; a crystallisingprocess may be found, for example, in U.S. Pat. No. 4,209,646), whereinthe bulk of the bisphenol contained therein is crystallised out (in thecase of bisphenol A, as adduct with phenol), separated by filtration,for example with a rotary filter, and washed with phenol. The water ofreaction and a little phenol is distilled off from the mother liquorcombined with the washing phenol; the distilled phenol is separated byextraction in the usual manner. The water is disposed of and the phenolis returned to the reaction. Phenol is now completely distilled off fromthe mother liquor in a vacuum. The bottoms obtained are mixed with abasic catalyst, metered continuously into a reactive rectification andtherein are decomposed at 190° C. to 270° C., preferably at 200° C. to260° C., particularly preferably at 210° C. to 250° C., and at 15 to 0.5mbar, preferably 12 to 1 mbar, particularly preferably 10 to 1 mbar. Thedistillate, consisting of phenol and isoalkenylphenol and its oligomers,is passed to the reaction. The bottoms, after acidification, are meteredinto a second reactive rectification which is similar to the previousone and therein are decomposed at 150° C. to 260° C., preferably at 160°C. to 250° C., particularly preferably at 170° C. to 240° C. and at thepressures given above, during which phenol distils off. This phenol,which may optionally be further processed through a column, is againintroduced into the reaction stream. Bottoms are withdrawn at the footof the column, and these are removed for disposal.

If the bottom component resulting from the basic decomposition, owing toa relatively small production run in a bisphenol plant, is too small forthe economical operation of one column, it is advisable to combine thesesmall quantities from several runs, or to collect the bottoms from oneplant to form a larger quantity and then to decompose this in a suitableapparatus.

By means of the process according to the invention, material yields ofup to 98% are obtained, provided that the water of reaction unavoidablyformed is removed from the material balance from the beginning. Inaddition, a particularly pure bisphenol is obtained.

The reaction mixtures leaving the series of reactors may contain, priorto the crystallisation, from 10 to 35 wt. %, preferably 12 to 32 wt. %and particularly preferably 14 to 30 wt. %, bisphenol. Should thecontent be unsuitable for a crystallisation, it can be adjusted byadding or distilling off phenol.

The process according to the invention, compared with the knownbisphenol processes, accordingly has the advantage that it produces avery pure bisphenol in excellent yield in a far simpler and whollycontinuous operation.

EXAMPLE

(cf. FIG. 1)

BPA was produced in the following manner in a series of three reactors,which were filled with acidic ion exchange material (SC 102, Bayer AG)containing as cocatalyst 3.6 wt. % dimethylthiazolidine.

5438 parts by weight per hour of phenol, together with one third perhour of a quantity of 274 parts by weight of fresh acetone and 402 partsby weight of decomposition product containing phenol andisopropenylphenol, with a loading of 0.6 kg/l catalyst per hour, wereconveyed into the first reactor at 50° C. The resulting reaction productwas mixed with an additional one third per hour of the above quantity ofacetone and decomposition product, tempered at 60° C. and passed intothe second reactor. After leaving the second reactor, the last one thirdper hour of the above quantity of acetone and decomposition product wasmixed into the reaction product, tempered at 70° C. and fed into thethird reactor. The loading rate was maintained at 0.6 kg/l×h for all thereactors. The acetone conversion was 97% to 98%.

This continuously operated apparatus for the production of bisphenol A(BPA) by the reaction, catalysed by acidic ion exchangers, of freshphenol, phenol from basic and acidic decomposition, acetone andisopropenylphenol from alkaline decomposition, yielded 6114 parts byweight per hour of reaction mixture having the composition I shown inTable 1, after the removal by distillation of residues of unreactedacetone (1) and optionally a filtration though a filter and basic ionexchanger (B) for the removal of acids leached out of the acidic ionexchanger.

By working up the reaction mixture in the conventional manner bycrystallisation (C), suction filtration, washing with phenol andpressing (F), a BPA-phenol adduct was obtained which, after flashdistillation of the phenol in the vacuum (D), yielded 983 parts byweight per hour BPA having a purity of 99.78%. The mother liquor andwashing phenol accumulating during the process were continuouslyevaporated in a vacuum (2,3); the phenol distilled off, after extraction(E) and separation of water and extracting agents (6,7), was readdedpartly to the reaction and partly to the washing stage; the high-boilingresidue, after 0.5 wt. % KOH had been homogeneously distributed therein,was metered as melt II at a rate of 425 parts by weight per hour into areactive rectification column having 20 trays (4), at an overheadtemperature of 80° C. to 82° C. and a temperature of 238° C. at thebottom and operated at 2 mbar. Distillate having the composition IIIdistilled over from this reactive column at a rate of 376 parts byweight per hour and flowed back into the reaction to produce BPA.Residue was discharged from the bottom of the column at a rate of 48parts by weight per hour. 2 mol toluenesulfonic acid per mol ofcontained KOH was added to this melted residue, which was then passedcontinuously into a reactive rectification column (5) likewise having 20trays, which was operated at an overhead temperature of approx. 73° C.to 76° C. and a temperature of approx. 205° C. at the bottom and at apressure of 5 mbar.

55 wt. % of the material introduced distilled over from this secondreactive column as distillate having the composition IV and 45 wt. % wasdischarged from the bottom as waste to be disposed of.

In the production of 983 parts by weight of BPA, 22 parts by weight ofwaste was therefore obtained, which corresponds to a material yield of97.8% (after prior withdrawal of the water from the condensation ofacetone and phenol).

TABLE 1 o,o- o,p- Tri- MG Σ Parts ′BP ′BP Chrom. BPA Ind. sph. 402 NPIPENP Phenol by wt/h I 0.09 5.06 0.22 93.72 0.16 0.60 0 0.14 0 0 6114 II0.19 16.10 0.51 75.76 020 2.10 0 1.22 0 3.91 425 III 0.02 0.05 0.06 0.380.01 0.01 0 0.01 52.01 47.32 376 IV 0.01 0.03 0.20 0.11 0.13 0 0 0.24 099.3 26

What is claimed is:
 1. A continuous process for producingdihydroxydiarylalkane in a series of at least two reactors comprising(i) reacting phenol with at least some ketone and at least someisoalkenylphenol at the lowest possible temperature in a first reactorto form a reaction mixture and continuing the reaction at increasingtemperatures in the succeeding at least one reactor and introducing atleast portions of the remaining ketone and isoalkenylphenol in said atleast one succeeding reactor to form at least one succeeding reactionmixture, and (ii) distilling off and removing unreacted ketone from thereaction mixture, and (iii) separating dihydroxydiarylalkane from thereaction mixture by crystallization to obtain mother liquor and crystalsand washing the crystals thus obtained with washing phenol, and (iv)combining the mother liquor with said washing phenol, distilling off thephenol and returning said phenol to the reaction, and (v) decomposingthe bottoms which include dihydroxydiarylalkane, isomers in the presenceof a catalytic quantity of base in a first reactive rectification toproduce (a) phenol and isoalkenylphenol distillate which leave at thetop and (b) high boiling residue at the bottom, and (vi) acidifying saidhigh boiling residue so that it contains a catalytic quantity of acid,and decomposing said residue in a second reactive rectification toproduce (c) phenol and (d) bottoms, and (vii) returning the phenolproduced in (vi) and the distillate produced in (v) to the reaction toproduce dihydroxydiarylalkane.